Located in north-central Washington State in a remote area of the Okanogan-Wenatchee National Forest, the Holden Mine was one of the largest copper mines operating in the US between 1937 and 1957. Producing over 90,000 tons of copper in its lifetime, the Holden Mine employed 62 miles of underground tunnels and left about 300,000 cubic meters of waste rock and 8.5 million tons of mill tailings covering 50 hectares of US National Forest land.
Our team was brought on to develop the detailed engineering design and remediate paste environmental problems at the mine. The multi-year, $200+ mine reclamation project was one of the larger cleanup sites in the State of Washington and required a high level of expertise in mine remediation. We conceived an integrated system of mine-closure components, including infrastructure improvements, groundwater collection and treatment, demolition, and a restoration approach to re-establish vegetation consistent with that of the surrounding forest.
Our team also helped by providing on-site quality assurance and oversight during the remedial action. Now, the Holden Mine lands and the adjacent forest can start the healing process, growing towards a greener future in Washington.